Wireless networks are increasingly employed to provide various communication functions including voice, video, packet data, messaging and the like, such as through use of wireless local area networks (WLANs) conforming to 802.11 standards established by The Institute of Electrical and Electronics Engineers. WLANs are often configured in an infrastructure network topology in which an access point (AP) coordinates communications for a number of associated stations (STAs) as well as providing management and control functions. However, another important network topology involves two or more STAs, or peers, that directly exchange information without the use of an AP as an intermediary. Such ad hoc networks rely on a peer to peer relationship between the stations. While peer to peer communications systems may provide greater convenience by avoiding the need for an AP, accommodations may be required to provide functionality that would otherwise be performed by a centralized control device.
Since many devices used in wireless communications systems are mobile, enhanced power management techniques are desirable to extend battery life. To this end, considerably effort has been expended in infrastructure networks to develop power saving techniques, many of which involve increasing the amount of time the STAs and AP may spend in low power modes of operation, known as sleep or doze modes. As with other network functions, a STA may coordinate entry and exit from a power save mode with its AP. In one power management strategy, a STA may asynchronously signal that it is entering a power save mode through the use of a power management message contained in a packet sent to the AP. Upon receipt of a power management message indicating the STA is in power save mode, the AP may buffer packets to be sent to the STA. The AP periodically transmits beacons with a traffic indication message (TIM) that may be used to indicate that data is ready to be transmitted to the STA. The period of time between beacon transmissions may be termed the beacon interval. The STA generally utilizes a period of time called the listen interval, corresponding to a plurality of beacon intervals, to coordinate its power save with the AP. The AP buffers data for the STA during the listen interval and the STA may awaken from power save mode to receive the beacon at the end of each listen interval. If the beacon indicates data is pending, the STA will initiate transfer of that data. Conversely, if no data is ready to be transmitted, the STA may return to power save mode.
In contrast, a peer to peer network lacks an AP for coordination of power management and may be unable to utilize the same strategies. For example, the high speed extensions in the BLUETOOTH® (Bluetooth) 3.0 specification enable two devices having WLAN radios communicating over a Bluetooth link to establish a Bluetooth Alternate MAC/PHY (AMP) link by using the WLAN radios in a peer to peer relationship. Implementation of the Bluetooth AMP link involves operation of the WLAN radios of both devices in an AP-like mode, including the continuous, periodic transmission of beacon frames while the AMP link is active. As a consequence, conventional power saving mechanisms for WLAN devices involving a device entering a power save mode for a period of time, such as the use of a power management message as described above, may not be employed while maintaining the AMP link. Further, since the beacon transmissions occur regardless of data transfer, this requirement may represent inefficient power consumption. For example, when network conditions result in periods when traffic is not being exchanged, such as when there is a delay in streaming from the backhaul and no data is being transferred over the AMP link, this power expenditure provides no benefit.
Other peer to peer communications systems, such as the WiFi Direct™ (WiFi Direct) protocol, may exhibit similar inefficiencies when the need to periodically transmit beacons interferes with the ability of a device to utilize power management strategies. Further, within the context of this disclosure, other network topologies may be considered to have analogous aspects to these peer to peer examples and similarly benefit from enhanced coordination of power save modes between network nodes. For example, a device may be configured to operate in a software-enabled access point mode to provide access point-like functionality. Such implementations are known as “softAPs.”
Accordingly, there is a need for coordinating power management between peers in a wireless communication system. The techniques of this disclosure satisfy this and other needs.